The Average Value Of $f ( x ) = \cos x$

Multiple Choice

The average value of $f ( x ) = \cos x$ on $\left[ 0 , \frac { \pi } { 6 } \right]$ is

A) $\frac { 2 } { \pi }$
B) $\frac { 3 } { \pi }$
C) $\frac { 4 } { \pi }$
D) $\frac { 5 } { \pi }$
E) $\frac { 6 } { \pi }$